Current Issue : October - December Volume : 2016 Issue Number : 4 Articles : 6 Articles
This article describes a new miniaturized omni-directional antenna with quasi-self-complementary\nstructure for wireless communication applications. A novel ground structure composed of\nfive rectangular plates is proposed to enhance the impedance bandwidth and reduce the antenna\nsize. The proposed antenna is comprised of two patches surrounded by the ground structure. Two\nmetal patches of the antenna are located on two opposite sides of the dielectric substrate. The feed\npatch is used to excite the radiation patch. This unique design is realized by properly choosing the\nsuitable feed patch shape, selecting similar slot shape on the radiation patch, and tuning their dimensions.\nThe proposed antenna with an extremely small size of 6 mm Ã?â?? 9 mm has an operating\nimpedance bandwidth ranging from 4.5 to 6.1 GHz for S11 < 10 dB, which also covers the two IEEE\n802.11a wireless local area network bands (5.15 - 5.35 GHz and 5.725 - 5.825 GHz). In addition to\nbe very small in size, the antenna exhibits omni-directional radiation patterns in the entire operating\nbandwidth and low cross polarization. The distortionless time domain performance of the\nantenna is confirmed by investigation of the phase response and group delay. The obtained results\nin both frequency and time domain show that the proposed antenna is suitable for use in wireless\ncommunication systems....
The detection and identification of ship targets navigating in coastal areas are essential in order to prevent maritime accidents\nand to take countermeasures against illegal activities. Usually, coastal radar systems are employed for the detection of vessels,\nwhereas noncooperative ship targets as well as ships not equipped with AIS transponders can be identified by means of dedicated\nactive radar imaging system by means of ISAR processing. In this work, we define a parasitic array receiver for ISAR imaging\npurposes based on the signal transmitted by an opportunistic coastal radar over its successive scans. In order to obtain the proper\ncross-range resolution, the physical aperture provided by the array is combined with the synthetic aperture provided by the target\nmotion. By properly designing the array of passive devices, the system is able to correctly observe the signal reflected from the\nships over successive scans of the coastal radar. Specifically, the upper bounded interelement spacing provides a correct angular\nsampling accordingly to the Nyquist theorem and the lower bounded number of elements of the array ensures the continuity of\nthe observation during multiple scans. An ad hoc focusing technique has been then proposed to provide the ISAR images of the\nships. Simulated analysis proved the effectiveness of the proposed system to provide top-view images of ship targets suitable for\nATR procedures....
GNSS�s orbit determinations always rely on ground station or intersatellite links (ISL). In the emergency of satellite-to-ground links\nand ISL break-off, BeiDou navigation satellite system (BDS) satellites cannot determine their orbits. In this paper, we propose to\nadd a spaceborne annular beam antenna for receiving the global positioning system (GPS) and global navigation satellite system\n(GLONASS) signals; therefore, the BDS satellites may be capable of determining their orbits by GPS/GLONASS signals. Firstly,\nthe spectrum selection, the power isolation, the range of Doppler frequency shift, and changing rate are taken into account for\nthe feasibility. Specifically, the L2 band signals are chosen for receiving and processing in order to prevent the overlapping of the\nreceiving and transmitting signals. Secondly, the minimum number of visible satellites (MNVS), carrier-to-noise ratio (...
A high performance robust beamforming scheme is proposed to combat model mismatch. Our method lies in the novel\nconstruction of interference-plus-noise (IPN) covariance matrix. The IPN covariance matrix consists of two parts. The first part\nis obtained by utilizing the Capon spectrum estimator integrated over a region separated from the direction of the desired signal\nand the second part is acquired by removing the desired signal component from the sample covariance matrix. Then a weighted\nsummation of these two parts is utilized to reconstruct the IPN matrix. Moreover, a steering vector estimation method based on\northogonal constraint is also proposed. In this method, the presumed steering vector is corrected via orthogonal constraint under\nthe condition where the estimation does not converge to any of the interference steering vectors. To further improve the proposed\nmethod in low signal-to-noise ratio (SNR), a hybrid method is proposed by incorporating the diagonal loading method into the\nIPN matrix reconstruction. Finally, various simulations are performed to demonstrate that the proposed beamformer provides\nstrong robustness against a variety of array mismatches. The output signal-to-interference-plus-noise ratio (SINR) improvement of\nthe beamformer due to the proposed method is significant....
We investigate the problem of minimizing the total power consumption under the\nconstraint of the signal-to-noise ratio (SNR) requirement for the physical layer multicasting system\nwith large-scale antenna arrays. In contrast with existing work, we explicitly consider both the\ntransmit power and the circuit power scaling with the number of antennas. The joint antenna\nselection and beamforming technique is proposed to minimize the total power consumption.\nThe problem is a challenging one, which aims to minimize the linear combination of 0-norm\nand 2-norm. To our best knowledge, this minimization problem has not yet been well solved.\nA random de cremental antenna selection algorithm is designed, which is further modified by\nan approximation of the minimal transmit power based on the asymptotic orthogonality of the\nchannels. Then, a more efficient de cremental antenna selection algorithm is proposed based on\nminimizing the 0 norm. Performance results show that the 0 norm minimization algorithm greatly\noutperforms the random selection algorithm in terms of the total power consumption and the\naverage run time....
The increase in global navigation satellite systems (GNSS) availability and services is fostering a new wave of applications related to\nsatellite navigation. Such increase is also followed by more and more threats, aiming at signal disruption. In order to fully exploit the\npotentialities of precise and reliable navigation, being able at the same time to counteract threats such as interference, jamming, and\nspoofing, smart antenna systems are being investigated worldwide, with the requirements of multiband operation and compactness.\nIn order to answer such need, the present work proposes a miniaturized dielectric resonator antenna (DRA) 2 Ã?â?? 2 array able to\noperate at E5/L5, L2, and E6 bands, with an overall footprint of only 3.5...
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